In 63 years of Disneyland, there has never been a precedent for restricting an IP to one area. That'd be foolish.
There may not have been a formal rule for keeping an IP in a single area, but it was never an issue at DLR until Buzz Lightyear Astro Blasters and Toy Story Midway Mania opened in 2005/08. Sure, there have always been some oddly-placed attractions (Babes in Toyland on Main Street, 20,000 Leagues in Tomorrowland 55) but they were confined to a single location within the park; it's not like the Swiss Family Robinson simultaneously had permanent locations in Adventureland and Bear Country. Attractions with a common source IP (Dumbo/Casey Jr, Alice/Teacups) have historically been located in proximity to one another.
I largely give entertainment and non-permanent meet & greets a pass in all this due to their temporary nature. It would be impractical to host a parade or have unstructured character interactions if all the animated characters were confined to Fantasyland. Since they're only present for a small portion of the operating day (and tend to get replaced with some regularity), it's easy to overlook thematic inconsistencies in favor of highlighting the atmosphere they provide. DLR also does a better job than most resorts of having area-appropriate live musicians throughout both parks, which helps to balance it out.
And while it's not DLR, Tokyo Disneyland and Tokyo Disneysea had very strict rules for which characters "live" in each park, with only Mickey and friends appearing in both. For example Stitch, most princesses, The Jungle Book characters, and the Aristocats live in TDL, while Bernard & Bianca, Ariel, Duffy and Aladdin live in TDS, and ne'er the twain shall meet. The rules were largely based on where the respective attractions and themed areas were located, but also extended to which characters could appear in meet & greets and entertainment in each park. These rules have been relaxed considerably for live appearances in recent years (again, after the introduction of TSMM with BLAB in separate parks) but each set of characters still has a clearly defined "home base" and only makes occasional appearances elsewhere.
Although there are a small handful of IPs that lend themselves to different interpretations in vastly different settings (like Indiana Jones, the Muppets, and-as much as I personally can't stand it-Toy Story), I think it should be largely avoided in order to make each area somewhat unique and worthwhile. WDW is falling into this trap with a permanent physical presence for The Little Mermaid, Frozen, Finding Nemo, Toy Story, and the Muppets in 2 parks each, and Beauty & the Beast will soon have a 3rd park to call home. The 4 parks used to have clear and distinct personalities which gave a vacation there a fairly diverse feel, but have become increasingly similar both in the types of experiences they offer and the IPs used to deliver them. Why bother spending the extra time and money to visit that other park, when we'll just see the same characters as the one we're in right now?